Light Frequency Issue

When photographing in artificial light, one has to always watch out for the potential light frequency issue. Due to the different intensities and wavelengths of light emitted by fluorescent and other sources of man-made light, there might be severe variations in exposure when photographing at fast shutter speeds. This is a similar “flickering” issue that you see when photographing or video-recording a TV screen – different light frequencies cause the flicker that is recorded by the camera. This can happen both when taking an image and when recording videos. Take a look at the following image, which I captured in a low-light situation using the Nikon Df:

Light Frequency Problem (1)

I took my family to a local park that was decorated with Christmas lights and snapped some photos. The weather was very cold outside (about 20°F) and when I looked at the photographs and saw the problem later that night, I thought that perhaps the shutter froze and somehow caused issues. Here is another photo from the same series, with a much better exposure, but still some visible flickering effect on the bottom of the image:

Light Frequency Problem (2)

I have seen flickering issues before, but none of them were as dark as on the first photo, so I did not think that it could be related to artificial light. When I initially posted this information on the site, asking if any other readers have encountered a similar problem (which I needed to gather for the upcoming Nikon Df review), a number of our readers, including experienced photographers like Bjørn Rørslett (who I am a big fan of) indicated that it had nothing to do with the shutter freezing, but rather with the A/C phase cycles. It was a good lesson learned for me. I decided to rewrite the article and post about this particular issue, so that others that encounter the same problem understand why it happens and know how to best deal with it. If you have read the original article, please accept my apologies for the provided information.

Source of the Problem

As explained in detail in this excellent article by Curtis Newport, artificial lights (especially of fluorescent type) emit light in different intensities and wavelengths. So the light source continuously changes in brightness and color temperature. Since the electrical current typically alternates at 60 cycles per second (60hz in US and Canada and 50hz in other countries), which basically translates to one cycle every 1/50-1/60 second, each cycle emits two pulses of light – one during the positive portion of the cycle and one during the negative portion, as shown in the below graph (courtesy of Scott Medling):

Light Intensity Chart

So if you are shooting at shutter speeds above 1/50-1/60, you could potentially “freeze” part of the cycle. In some cases, it could be at peak intensity as on the second photo above, while in others it could be at middle of the cycle where the light output is very dim, as in the first photo.

Take a look at the second set of photos, captured in an indoor environment:

Light Frequency Problem (3)

Light Frequency Problem (4)

Both images were shot in manual mode with identical settings. And yet the difference in exposure and color temperature throughout the image is apparent between the two. You can see the gradient “flickering” clearly, especially on the lower part of the frame.

This problem is only likely to be affected by gas and/or “cold” lighting, such as fluorescent or mercury vapor bulbs. Hot lighting generated through typical filament bulbs will not cause such issues in your images. Typically, energy-efficient lighting is moving more towards “cold” lighting solutions, which means that this problem could become more evident as the world moves forward (thanks to Scott in comment #10 for extra information).

How to deal with the problem

There are basically two ways to deal with the above problem. One way is to set the shutter speed at 1/60 of a second in the US/Canada (or 1/50 in other countries), which should catch a full cycle, resulting in even exposure. Setting the shutter speed to 1/125 of a second should also work (1/100 in other countries), since you catch half of the cycle. You have to be careful with anything faster, slower or in between, since those can potentially record inconsistent illumination of light throughout the frame. If you need to keep the shutter speed above 1/125, the best way to deal with the issue is to use flash that overpowers the artificial light. Just make sure that your shutter speed is not set above the flash sync speed (typically 1/200 – 1/250) when using a focal plane shutter, since that can also partially darken the image similar to the examples provided above.


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Avatar of Nasim Mansurov About Nasim Mansurov

is a professional photographer based out of Denver, Colorado. He is the author and founder of Photography Life, along with a number of other online resources. Read more about Nasim here.

Comments

  1. 1
    ) Randall

    Can you try shooting more subjects with bright light sources in background and dim foreground. Like say a person in front of a bright window in a darker room? Or a bright lamp in a dark room. The reason I say is my d600 has a similar “exposure” issue I never experienced on any other camera I think has to do with the exposure or aperture lever.

    • Randall, I have many different images and some that were shot against very bright light sources. Your D600 issue is a little different I think – could be a faulty aperture lever on the camera.

      • 4
        ) Randall

        Well after 5 trips to Nikon for this exposure and dust issues and being on my third shutter replacement Nikon management called and said the camera is to good to their “specifications”. So I wish you luck in solving your problem. ;) As for Nikon I wish them luck in the future considering while window shopping for the 58 1.4g and almost dropped 8k switching to canon (5d mk III, 24-70 2.8 II, and 85 1.2 II). After shooting the 58 1.4g and 85mm 1.2l back to back it was very tempting. Especially after what I have been through with Nikon. Still on the fence…

  2. 3
    ) Bjørn Rørslett

    I’ve been shooting the Df for many months now and in ambient temperatures -20C or colder. Never had a sticky shutter so simply don’t buy the ‘lubricant freezing’ hypothesis.

    As the lights here are man-made there is with certainty a frequency variation from A/C phase cycles. You could easily have caught different phases and thus get uneven exposures. Try lowering the shutter speed to below 1/50 sec.

    When you live in a Nordic country with low light half the year, the cycling of A/C shows up in pictures in many unexpected ways. A typical example is the vertical ‘venetian blind’ appearance when you shoot falling snow, a street light is present, and the shutter speed is very long. This results from A/C cycling as the snow falls literally through the angle covered by the lens.

    • Bjørn, thank you so much for commenting on this – I am your huge fan!

      Regarding this shutter freezing situation, since the lights were all different in this particular case, is it possible that it was not related to man-made lights? Isn’t the flicker supposed to show a small variance in exposure rather than almost pitch-black variance as shown in the first photo?

      • 6
        ) Bjørn Rørslett

        At very fast shutter speeds you can observe *huge* variation in exposure due to A/C cycling, if ambient natural light levels themselves are low.

        Normally, if these lights are hooked up to different power outlets, there will be a phase mixture to even out the overall exposure. There is *no* guarantee for an even illumination though, unless you shoot at so slow speed that light have done at least a full frequency cycle (ie. 1/50 or 1/60 sec).

        An unmentioned source for variation is of course using a “G” lens and controlling the aperture by the command wheel of the camera, but this error in itself typically is < 1/3 stop and rarely noticeable unless you do single-frame animated filming.

        • Thank you Bjørn for clarifying this. The huge variation is rather surprising to me, but it explains why this happens. I have completely rewritten the article and its title to reflect this. Hopefully it will help other readers to understand this issue when they encounter it.

          P.S. So far I love the Df as well. There are a couple of things I don’t like ergonomically (the grip is small, the odd location of the “ears” for the camera strap), but other than that, it is excellent, especially when it comes to image quality.

  3. 8
    ) Grey

    Good post. Thank you for clearing this up. And thanks to Bjorn – your knowledge is inspiring.

  4. 9
    ) Matt

    I learned about A/C cycling the first time I had to shoot volleyball on assignment at our local high school “B” gym. I’ve never seen such bad lighting in my life. Even looking at the lights with the naked eye, you can see that they vary in color. Some are a dull orange, others blue, and some white. They don’t cycle in sync with each other, so the end result is that my white balance can change multiple times in each series. I also get the flickering effect where half of a picture will be much darker than the other half.

    Since I have to shoot at least 1/500 and flash is prohibited, I have just had to deal with it. I’ve talked with volleyball parents and we have joked about holding a fundraiser to buy the school some new lighting!

  5. 10
    ) Scott

    Good on you to correct your previous article on your dark photos issue. There are a few other points that you could include, to provide more clarity. World-wide, many countries use 50 rather than 60hz, so any calculations for shutter speed should take into account the local conditions. Secondly, this problem is only likely to be affected by gas and/or “cold” lighting, such as flourescent or mercury vapour bulbs. Hot lighting generated through typical filament bulbs will not cause such such issues in your images. Typically, energy-efficient lighting is moving more and more towards “cold” lighting solutions, which means that this problem could become more evident as the world moves forward.

    • Excellent info, thank you Scott! If you do not mind, I added a few sentences from the above comment to the article.

    • 19
      ) Jon

      Actually, energy-efficient fluorescent systems (including compact fluorescent lamps, CFL) typically use electronic ballasts that operate the lamp at much higher frequencies than the mains. Fluorescent lamps are more efficient at the higher frequencies, and this also eliminates the large inductive ballast that is one of the inefficiencies in traditional fluorescent lighting. That means the situation going forward is actually getting better, not worse. I see this all the time in sports shooting. Gyms that have the older systems and that exhibit the flickering experienced by Nasim are being upgraded or replaced with newer, electronic fluorescent systems that don’t exhibit the problem.

  6. 11
    ) HomoSapiensWannaBe

    Very interesting article!

    1.) I read somewhere that if the shutter speed is an even multiple of the AC frequency, you are less likely to experience this problem, and the longer the shutter speed, the more the cycling averages out and eventually doesn’t matter. Therefore, for 60 cycles, the series 1/60, 1/30, 1/15, 1/8, 1/4, etc. gets more and more likely to produce an even exposure. Using 1/125th introduces more risk because you don’t capture a full cycle, but is better than 1/100th or 1/160th.

    2.) Are LED lights susceptible to this effect?

    • 13
      ) Arthur

      1.) I don’t know

      2.) No.

    • Looks like that’s the case – please see the updated chart provided by Scott Medling.

      In regards to LED light, as far as I know those are not prone to the flickering issue.

      • 31
        ) Daham

        Simply they do when powered by an A/C source but neither with a A/C converted to D/C smoothed and regulated nor a D/C . As a/c source is fluctuating (varying) it’s Voltage and polarity periodically and LEDs let current to flow to a one direction only,so LED may have flickering (when connected to A/C just in series with a resistor).Ask some one very good on electronics to build a circuit to connect a single LED just directly to the mains- 110V in US and 230V for me, and shoot the powered bulb in the burst mode with a greater shutter speed than 1/250 or with a high speed video camera ( Nikon 1 AW 1′s Slow-motion movie option would do the job)

        P.S- DON’T PLAY WITH HIGH VOLTAGEs !!!!!!!!!!

      • I’d like to Comment on the LED. My qualifications of Sorts. I studied Electronic and received a Diploma in Home Electronic Entertainment Equipment Servicing. And Worked in the Electronics Field for about 30 years.

        A LED is a Light Emitting Diode. A Diode only allow current (and Voltage) flow in one direction. A LED is a specialize diode that has been processed with an element that Lights or Fluoresces when current flows through it.

        An LED doesn’t pulse as the voltage is adjusted. Depending on the processing they have certain Limits of when they begin to fluoresce and the maximum voltage and current which create Maximum brightness.

  7. 12
    ) Scott M

    Actually, your best bet is to set the shutter speed equal to multiples of half the voltage period in your area. This is because the period of the voltage power is half that of the electricity voltage (since P = V^2/R). Note that this does include setting it to the voltage period. So rather than being limited to 1/60 or less you’re limited to 1/125, 1/60, 1/40, or less (or if you’re in a 50Hz area, you’re limited to 1/100, 1/50, 1/30, or less).

    If you’re visiting a foreign country, check the frequency there. If you’re in N. or S. America it’s probably 60Hz; if you’re not, it’s probably 50Hz. If you set the shutter speed to a 1/3 of a stop faster than you should (ie. 1/60 or 1/125 when it should be 1/50 or 1/100), you may get exposures varying by up to 1/2 an EV. But if you set the shutter speed to 1/3 of a stop slower (ie. 1/50 or 1/100 instead of 1/60 or 1/125), it’s possible you’ll get variations of up to 1/3 an EV.

    • Scott, thank you for the information and the chart that you have provided! I updated the article with it.

  8. 14
    ) JamesT

    Now, that’s how the Internet *should* work! Nice to see a civilized sharing of ideas and information. Very informative post.

    One other place where this phenomenon is a big challenge is shooting indoor sports without a flash, especially under mercury lamps. Not only do they power cycle, but they also vary in color temperature as the waveform cycles, wreaking havoc with white balance. Leaned this the hard way by trying to do a preset white balance for an event. Not a good idea, resulting in everything being very off. At least with auto WB you have a chance of getting it correct.

  9. 20
    ) Carmelo

    Hallo Nasim, thank you very much for this very interesting article! This “artificial light” issue is unfortunately very common. But I seldom pay attention to it during my photo sessions. And if the exposure seems not to be good, it’s always possible to correct the picture during postprocessing… :-)

    • 21
      ) Carmelo

      Nasim, the power of the web is the great possibility to share experiences and together to achieve a better knowledge of the matter. The correction of your first article about this issue is exemplary. I look forward to your comparison between Nikon D600 and Nikon Df!

  10. 22
    ) Carsten

    Next to last weekend I seemingly stumbled across this issue when trying to AF fine tune my D800 to a 105 mm Micro-Nikkor using LensAlign and FocusTune: as it is winter now I shot indoors, lighting with two halogen bulbs, 230 V, 50 Hz, 50 W each, with a shutter speed of 1/800 at f=2.8, ISO 1000. Besides some other issues (e.g. to much noise because of the low light, wrong WB etc.) there were considerable variations in exposure from one shot to the user, though not comparable to Nasim’s first example shown above, rendering the shots almost useless for the task.

    Micheal Tapes suggested that these variations in exposure are caused by the 50 Hz A/C frequency.

    I still wonder if this could be the case, as halogen (filament) bulbs like conventional wolfram filament bulbs are supposed not to have any flicker.

    BTW: I used manual exposure mode, and the 105 mm Micro-Nikkor is a “G” lens.

    Any hypotheses or explations?

  11. 23
    ) Jorge Balarin

    Not a problem for Nikon. The will launch the DF-x as an “update”, and the ones that bought tze DF will be stuck with their bad copies : )

  12. 24
    ) BDJ

    Keep in mind that not all electrical lights flicker with AC cycles. LED lighting uses DC electricity and doesn’t flicker. Incandescent bulbs are on AC, but emit light based on heating a filament and that filament doesn’t cool fast enough to dim between cycles, so it doesn’t flicker. Fluorescent lighting is probably the only really problematic one – maybe street lights that use sodium bulbs too.

  13. 25
    ) jfp

    Excuse my ignorance, and perhaps this has already been answered and I missed it, but is this “problem” or issue restricted to the use of the Df or is this an issue that can be experienced with all cameras? Thanks in advance.

    • JFP, this can happen to any camera, not just Df.

  14. 27
    ) Cecilio

    Hi Nasim,

    Just a question. I suppose that this problem only happens when shooting without flash. Is it true? Can it happens also with flash light?

    Thanks in advance.

    Regards from Spain!!!

    • Cecilio, yes, it mostly happens without flash. If you use flash and it is powerful enough to overpower the ambient light, then you will not see such issues in your images…

  15. 29
    ) Joy Yagid

    I found this out with LED Christmas lights – while someone up thread mentions that LED’s don’t cycle – I have photos that say otherwise.

    • 30
      ) Jon

      Whether LED lights cycle depends on how they are powered. Most are operated from DC and won’t cycle. In some low-cost applications such as Christmas lights, they may be operated from rectified, unfiltered AC and then they’ll cycle.

      • 33
        ) BDJ

        This is something I hadn’t thought of in my post. I’ve only worked with LEDs on true DC, but I could definitely see companies doing rectification only for cheap implementations and getting flickering. In that case, the flickering should be at 120Hz instead of 60hz.

    • 35
      ) Erik

      LED lamps that dims may be a thing to look out for in the future, because they are fed with a chopped up DC (so called pulse width modulation or PWM). So in reality they do not dim per se, they just are’nt lit that often during a fraction of a second.

  16. 32
    ) Rolando Rios

    Hi Nassim,
    I am an electrical engineer, enthusiastic photograph for more than 40 years and big fan of your site that I enjoy very much.
    I have a couple of observations regarding your very interesting article about light frequency:
    Curtis Newport is right, fluorescent light behaves as a strobe pulsing according to power cycles (120 Hz in Noth America), so if you are shooting at shutter speeds above 1/120 you get only a part of the cycle and you don’t know which one.
    Then your advice: “You have to be careful with anything faster, slower or in between”, is not entirely correct, It’s just faster speed that could cause problems because you catch only an undetermined part of the power cycle. Slower speeds will catch more than one power cycle, and the more, the better.
    By the way, this problem is in fact related with your Df because it can be used at high ISO settings, allowing shutter speeds bigger than 1/120 sec in dim fluorescent light.

    • 34
      ) Scott M

      Rolando,

      Technically, only integer multiples of the power frequency (120Hz or 100Hz) will show abolsutely no flickering. Obviously speeds faster than it will be a big problem. The speeds in between the period (ie. 1/120) and twice the period (ie. 1/60) should be avoided because there is variation; it’s just not as pronounced. At some point (1/25 for 60Hz) you’re keeping the shutter open for so many cycles that a fraction of a cycle just doesn’t matter any more for normal precision. For 50Hz, I think everything slower than 1/30 is an integer multiple (depending on how the camera actually handles 1/13; is it 1/12.5?)

      Since you’re an EE, I’ll list some of the worst cases for 60Hz (math format is for WolframAlpha):
      1/125 is as close as possible to 1 cycle (but still up to 0.12EV variation)
      1/100 is bad; log2(Int[sin(x)^2,1.5,1.5+pi*120/100]/Int[sin(x)^2,0,0+pi*120/100]) = 0.38EV
      1/80 is bad; log2(Int[sin(x)^2,1,1+pi*120/80]/Int[sin(x)^2,2,2+pi*120/80]) = 0.51 EV
      1/60 = 2 cycles
      1/50 is bad; log2(Int[sin(x)^2,1,1+pi*120/50]/Int[sin(x)^2,2.5,2.5+pi*120/50]) = 0.36EV
      1/40 = 3 cycles
      1/30 = 4 cycles
      1/25 is ok; log2(Int[sin(x)^2,0,0+pi*120/25]/Int[sin(x)^2,1.5,1.5+pi*120/25]) = 0.09EV
      1/20 = 6 cycles
      1/15 = 8 cycles
      1/13 is ok; log2(Int[sin(x)^2,1,1+pi*120/13]/Int[sin(x)^2,0,0+pi*120/13]) = 0.05EV
      1/10 and nearly everything slower is an integer multiple of 1/120.

      Obviously, this is complicated, so a simpler rule is:
      For 60Hz: use 1/125, 1/60, 1/40, or slower.
      For 50Hz, use 1/100, 1/50, 1/25, or slower.

  17. Here is another tutorial you can do at home, “Painting With Light”. It is an age old (and really fun) photography technique based on actively manipulating the light in a scene during a long exposure. It can be done in a variety of settings from studios to outdoors, and a variety of styles from macro to nature. http://shutterbugremote.com/painting-with-light-a-tutorial-you-can-do-at-home/

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